Sunday morning at the Foro Italico in Rome and the 37-year-old Thomas Muster, the 1995 French Open champion and the outstanding clay-court player of his generation with 40 titles, was getting in a little gentle practice before his veterans' Delta Tour of Champions final against Jim Courier.

His hitting partner, dressed in red shorts, a plain white short-sleeved shirt and white baseball cap was a fellow left-hander of no obvious distinction, and who appeared rather stiff in the joints and a touch less than enthusiastic.

Midway through the mildest of rallies Muster looped a backhand short and, with a sudden, uncharacteristically rapid dart forward, the other man whacked a forehand deep into the corner, the ball fizzing and thudding into the advertising hoardings. As he turned he lifted his cap and his long black hair spilled out to shoulder length. It was like suddenly recognising a policeman in civvies. It was Rafael Nadal.

Mention of his name and the image is instant. White pirate length trousers, or clamdiggers as the Americans call them, sleeveless orange shirt, and white bandanna. The 18-year-old Spaniard has taken the tennis world by storm this year, rushing up the rankings to No5 in winning five tournaments, including two Masters Series titles in Monte Carlo and Rome.

He could be forgiven for looking a little jaded as he practised with Muster on the morning of the Italian Open final, for he had just completed a 16-match winning streak on clay. Yet any doubts about his stamina were dismissed that afternoon when, in the most wonderfully dramatic of matches, he defeated Argentina's Guillermo Coria, last year's French Open runner-up, over five sets lasting more than five hours.

"This guy has such a sharp mind. He's so focused on tennis and he so wants to win," said the admiring Muster, who admitted to seeing a mirror image of himself when hitting with Nadal.

"Everything he does turns around tennis and that's exactly the attitude you need."

Muster shares the view, widely held, that Nadal will not merely be a great Spanish player, or a great clay-court player, but one of the world's all-time greats. "What he has is unusual and rare. He has that determination and willpower that singles him out."

The intensity of Nadal's play is almost frightening. His speed around the court is phenomenal, even by the standards of Australia's Lleyton Hewitt, while his forehand is devastating. "Against a right-hander he will kill them with that forehand. They are going to jump out of the stadium," said Goran Ivanisevic, the 2001 Wimbledon champion.

"It's a huge shot," admits Roger Federer, the current world No1 whose own full-powered forehand is a wonder to behold. "Rafael is an outstanding athlete as well and moves totally differently to most players. Yet even on the run he can hit with spin."

"I've not seen another player like him since Boris Becker. He's a real pearl," said Ion Tiriac, who guided the German prodigy in his formative years. That said, there is more of the kid about Nadal than Becker.

Tennis is up to the gills in youngsters who look terrific from the baseline in practice, but what has singled out Nadal, who will be 19 a week next Friday, is his ability to embrace the big occasion at such a young age and with such unfettered exuberance. There are fist pumps, scissors kicks and huge joyous leaps off the ground - though for the most part any overt intimidation is restricted to his shots.

Unlike Hewitt there is nothing of the brat. Nadal's enthusiasm is endearing and, if his steadfast aggression is atypical of Spanish players, then it was integral to his game from an early age. Sergi Bruguera (twice), Carlos Moya, Albert Costa and Juan Carlos Ferrero have all won the French Open title since 1993 but all, in their different ways, have epitomised a somewhat reserved and self-contained persona.

Nadal, in sharp contrast, is outgoing and gregarious. When he beat Andy Roddick to give Spain what proved to be a decisive 2-0 lead in the Davis Cup final last year, Moya sagely remarked: "He's the kind of guy that likes to play these kind of matches. So I really trust him. I believe in him."

His father's brother, Miguel Angel Nadal, was a defender for Spain, for whom the word uncompromising might have been coined (his nickname was the Beast of Barcelona) while his other paternal uncle and coach, Toni, gave "Rafa" his first racket when he was four: "I was a defensive player and not all that successful, so the idea was for Rafael to be aggressive. As it turned out, that style fitted his personality perfectly."

When Nadal was 14, the Spanish federation suggested he move to Barcelona. But his parents declined, wanting to remain involved in their oldest child's education. Staying in his native Majorca meant Nadal received less financial support but his father, a successful businessman, was prepared to pay for training.

At 15, Nadal won his first Tour-level match, beating the Paraguayan veteran Ramon Delgado in the opening round of the ATP event in Majorca in 2002. And so the wheel of success began to spin. There have been setbacks, including elbow and foot injuries that prevented him playing at Roland Garros for the past two years. Now, suddenly, he is this year's French Open favourite without having played there and having not gone beyond the fourth round of any major.

Muster sounds a word of caution. "Now it's the next step. He has to deal with all the pressure of being the favourite and it's a lot for a young brain to cope with. Some players become negative about it, some are very positive. You never know, so that's what we have all still got to see with Rafael. But his potential is just enormous."

Teenage Tennis Champions

Boris Becker As a fresh-faced 17-year-old in 1985 the German won Wimbledon at his second attempt. Retained title the next year and went on to win four more majors but never got beyond the semi-finals of the French.

Bjorn Borg Won the French Open title at the second attempt as an 18-year-old and retained it as a teenager, the second of six triumphs at Roland Garros. Equally at home on grass, he won the Wimbledon title five times, doubling with the French from 1978-80.

Michael Chang Won his only grand slam title, the French, as a 17-year-old in 1989, the youngest male winner of a major. Runner-up at Roland Garros in 1995 and in the Australian and US Opens the next year.

Ken Rosewall Won the Australian and French Open titles as an 18-year-old in 1953. Winner of eight grand slam titles in total, although never Wimbledon where he was runner-up four times.

Mats Wilander Won the French as a 17-year-old in 1982, the first of three titles at Roland Garros and seven grand slam titles in all, although never Wimbledon where he failed to get beyond the quarter-finals.

Pete Sampras Won the first of his 14 grand slam titles at Flushing Meadows as a 19-year-old in 1990 when he became the youngest US Open champion since the previous century. Best at Roland Garros was semi-final.

Stefan Edberg Won the Australian Open as a 19-year-old in 1985, the first of his six grand slam titles. Best at Roland Garros was runner-up in 1989.